The present invention relates to an electrophotographic recording apparatus including a charging roller for charging the photosensitive drum to a desired potential, and more particularly to an electrophotographic recording apparatus in which the circumferential speed of the charging roller to the circumferential speed of the photosensitive drum is greater than 1.
The conventional electrophotographic recording apparatus, such as a, printer or a duplicator, generally includes a photosensitive drum having a rotation shaft, and a charging roller having a rotation shaft substantially parallel with the rotation shaft of the photosensitive drum and also holding its own external circumferential surface in contact with the external circumferential surface of the photosensitive drum to thereby give a static charge to the external circumferential surface of the photosensitive drum.
The above-mentioned electrophotographic recording apparatus further includes a developing section for supplying a toner to the statically charged external circumferential surface of the photosensitive drum, and a cleaning section for removing the toner remaining on the photosensitive drum which toner was not transferred to a recording paper. Among the techniques for cleaning the photosensitive drum by the cleaning section, there is a recycle system in which the toner recovered from the photosensitive drum by the cleaning section is returned to the photosensitive drum by the cleaning section, and the toner is carried by the rotating photosensitive drum and collected in the developing section.
In the recycle-system electrophotographic recording apparatus, the greater part of the normally charged toner is removed by the cleaning section oppositely charged with respect to the polarity of the charge on the toner. A small amount of the toner which is opposite in polarity to the greater part of the toner remains on the photosensitive drum and passes through the cleaning section.
In the recycle-system electrophotographic recording apparatus, when the small amount of the toner that has passed through the cleaning section enters between the charging roller and the photosensitive drum, the small amount of the toner adheres to the external circumferential surface of the charging roller, thus producing a so-called filming phenomenon. When the filming phenomenon occurs, the resistance value of the charging roller increases due to the toner adhesion, making it difficult for the charging roller to give a sufficient amount of charge to the photosensitive drum to enable stable printing. To prevent the photosensitive drum from being insufficiently charged, the charging roller is rotated faster than the photosensitive drum to thereby reduce chances that the small amount of the toner enters between the charging roller and the photosensitive drum.
In the recycle-system electrophotographic recording apparatus, however, because the charging roller is rotated faster than the photosensitive drum, by triboelectricity produced between the charging roller and the photosensitive drum, the photosensitive drum is charged to a potential so high as to lead to unstable printing during operation for a long period of time. This results in poor quality printing, which has been a problem.